The present invention relates generally to methods and apparatus for measuring the air permeability of wall-like or sheet-like elements, such as a felt or wire used in paper machines.
In particular, the invention relates to air permeability measurement methods and apparatus wherein a measurement head including a blower having an air discharge nozzle, a blade wheel and a motor for rotating the blade wheel is used and wherein the measurement head is situated with the blower nozzle tightly engaging one of the surfaces of the element whose permeability is to be measured whereupon a volumetric air flow through the element is produced.
Measurement of the air permeability of various air permeable fabrics is often required. For example, the permeability of felts and drying wires of the type used in paper machines, filter elements, and the like, must be measured on a periodic basis to ascertain their condition. Such air permeability measurements must be performed in industrial environments and usually on the very sites at which the elements are used. For example, permeability meters are usually part of the standard equipment of every paper mill so that the permeability of plastic wires used in the paper machines can be measured periodically. Such plastic wires tend to become obstructed by dust or other contaminants or through a reduction in the mesh size of the wire screen during use. The machine operators must be aware of the fabric permeability since it is extremely important, such as in the case of drying wires of paper machines, to maintain a certain minimum permeability to assure proper operation of, for example, pocket ventilation devices and the like. A wire of a paper machine or a filter fabric of a filter device must be replaced or cleaned based on the permeability measurements. The proper operation of fabric cleaning or washing devices is also monitored through the measurement of the permeability of the elements upon which such devices operate.